1. Field of the Invention
The present invention relates to towed fiber optic acoustic arrays. More particularly, this invention pertains to a harness for containing and directing the various conductors associated with a towed array for measuring acoustic signals.
2. Description of the Prior Art
Hydrophones of fiber optic design are advantageously employed, for example, to detect the presence of submerged objects and to conduct underwater seismic studies. Such devices operate upon the interferometer principle with the path of an input beam split between reference and sensing paths. Such paths are created by winding fibers upon physically separate mandrels, one of which is dimensionally-unaffected by and the other of which is affected by pressure variations. See, for example, U.S. Pat. No. 5,317,544 of Maas et al. for xe2x80x9cMultiple Segment Fiber Optic Hydrophone.xe2x80x9d Hydrophones are commonly deployed in geometrical arrays for generating a plurality of spatially-distributed data points. Such distributed data may be analyzed to enhance reliability via averaging techniques, to determine direction of travel and to generate object profiles or xe2x80x9cshadows.xe2x80x9d
A conventional hydrophone array or the above-described type is illustrated schematically in FIG. 1. As shown, an input pulse 10 is launched through a fiber optic transmission line from a gated laser source 12 toward a series of separate fiber optic interferometer sensors configured, for example, as hydrophones 14 arranged in parallel between an input transmission line 16 and a return line 18. With suitable delays in the fiber optic network, the single input light pulse is divided up among the interferometer sensing elements. The pulse 10 is split in the case of each hydrophone interferometer between a reference path (indicated xe2x80x9cAxe2x80x9d) and a sensing path (indicated xe2x80x9cBxe2x80x9d). An output light pulse with appropriate pulse amplitude-modulated acoustic information encoded thereon is associated with each sensing element. The output light pulses are coupled sequentially onto a return fiber optic transmission line that communicates with a photodiode receiver 20 and associated signal processing electronics 22. Thus, one input light pulse 10 is converted into a train of light pulses 24 equal to the number of sensors.
The time duration of the output pulse train 26 governs the repetition rate of the input pulse 10. After one output pulse train is received, it is closely followed by another derived from a second input pulse. The duty cycle of the input pulse train is low. (It can equal 1/N where N is the number of sensors interrogated without overlapping of adjacent output pulses.)
The complete assembly of a linear towed array requires the integration of numerous elements into a xe2x80x9cpackagexe2x80x9d suitable for the intended environment and use. Such assembly must necessarily incorporate an often quite large plurality of hydrophones, associated optical (e.g., couplers, splices, delay lines, etc.) and electronic (e.g., amplifiers, multiplexers, etc.) elements as well as conductors, both optical and electrical, for facilitating the necessary communication of signals between such devices and (often very) remote ship-based apparatus such as a laser source, photodetector, multiplexer and other signal processing devices. The assembly may be somewhat simplified by the use of modular assemblies that package a number of elements, often similar in size to the hydrophones themselves. An example of such a modular arrangement is taught in pending U.S. patent application Ser. No. 09/362,768 of Goldner et al. titled xe2x80x9cFiber Optic Component Assembly System.xe2x80x9d
The selective interconnection of optical and electronic elements required to form a complete fiber optic towed array system necessarily demands the further packaging of numerous electrical and optical cables and fibers and the coupling thereof to a predetermined system element. The complete assembly of such an extensive system is a daunting task. Additionally, the various signal conductors are individually relatively fragile and therefore vulnerable and require that packaging arrangements take into account the significant stresses that can be exerted by the deployment of an underwater array that may attain a mile or more in length.
Prior art apparatus for delivering optical and electrical conductors to the devices that comprise a hydrophone array have relied upon standard cabled fiber, often bundled with copper cabling. The use of such arrangements results in relatively high cost of next-level assembly. That is, such arrangements require the stripping of outer and inner plastic (and other) sheathing materials, as well as complicating identification of individual fibers within an often large cabled set.
The preceding and other shortcomings of the prior art are addressed by the present invention that provides a telemetry harness for supporting a plurality of conductors for conductive interconnection with aligned sensors and modules of a segment of a towed array. Such harness includes an elongated flexible member of woven fabric. A plurality of optical fibers is fixed to and arranged generally longitudinally with respect to the fabric.